The invention concerns a method of inserting a message in an image, characterized in that it comprises the steps of: selecting a set of points in the image as a function of predetermined criteria, so as to form a coordinate system in the image, calculating (S21) an affine transformation between a predetermined coordinate system and the coordinate system formed in the image, generating (S24) a pseudo-random sequence for each symbol of the message to be inserted, in the predetermined coordinate system, projecting (E25) each pseudo-random sequence into the coordinate system formed in the image, by affine transformation, inserting (S27) each symbol of the message to be inserted, as a function of its respective projected pseudo-random sequence.